Dynamic memory devices employ sense amplifiers which detect the amount of charge stored in a memory cell by sensing a small change in voltage on a bitline to which the memory cell is connected. Because a large number of cells are connected to each bitline, and since the size of the memory cells have been decreased as the storage capacities have increased, the voltage change on the bitline attributable to the charge stored in the memory cell is very small. Therefore, sense amplifiers must be isolated from the bitlines during read operations in order to prevent noise on the bitline from affecting the sensing operation.
Previously developed sense amplifiers use an N channel transistor to isolate the bitlines from the sense amplifier. The "T signal" used to switch the N channel transistors on and off produces random noise, which may upset the balance of the sense amplifier. Thus, the means of isolating the sense amplifier from the bitlines contributes to additional random noise.
Aside from random noise, the bitlines also couple a high capacitance to the sense amplifier which reduces the sensing speed. Therefore, it is desirable to uncouple the sensing amplifier from the bitlines as soon as the sensing amplifier has locked in the appropriate signals. The previously developed sensing amplifier circuits are not capable of automatically isolating the amplifier, and therefore, inhibit the sensing speed.
Therefore, a need has arisen for a sensing amplifier circuit which effectively isolates the sensing amplifier from the bitlines of a dynamic memory array once the appropriate data value has been latched by the sense amplifier.